1. Technical Field of the Invention
The invention concerns a sealing mat for use in civil and underground engineering for the insulation of soil against liquids, especially water, having two outer layers comprising a fibrous material, between which is inserted a powder of mineral sealing material, e.g. bentonite, and the two layers are connected to each other.
2. Description of the Prior Art
In the most varied fields and civil and underground engineering works the fundamental necessity often exists of sealing against liquids or preventing liquids from spreading in the ground and from time to time to partition a defined volume of soil as regards moisture. In this way, in the case of waste dumps, contaminated soils and similar, it is necessary to ensure that no leakage water and other moisture enters into the ground lying beneath and above all not into the ground water where it can lead to serious pollution, unusability and even the poisoning of drinking water. The problem of sufficient sealing also arises in the case of ponds, sewage plants, storage reservoirs, canals, etc. For this purpose it is known to place a foil into the ground which ensures absolutely that liquids, and in particular water, are prevented from spreading. Besides plastic, it is also common to employ mineral sealing materials. The use of double-layered formed fabrics is known between which bentonite is inserted in a powder form as a mineral sealing material. The connection between the two formed fabrics is achieved through a needle bond. Bentonite is easy to handle and develops its waterproofing quality only when water is added, when it swells up and changes to a jelly-like substance. Whereby producing a film that is impervious to liquids. The use of this kind of sealing mat provided with bentonite as a mineral sealing material has found wide use in civil and underground engineering.
However, it proves a considerable disadvantage that the mats are are not laid out horizontally but as a rule at an angle oblique to the horizontal line. This causes shearing loads which are effective tangentially to the top surface of the sealing mat, thus frequently producing relative displacement of the two layers, considerably favored by the fact that in the presence of moisture the bentonite forms a jelly-like substance between the two formed fabrics and as a consequence a correspondingly lower coefficient of friction occurs, so that almost all the shearing force must be compensated for by the needle bond of the two formed fabrics. The forces that can be absorbed by this are comparatively low so that the shearing force created leads comparatively frequently to relative movement of the two formed fabrics. Both formed fabrics thus shift relatively to each other.